The present invention is directed to a method of inhibiting drying shrinkage of and cracking with respect to structural concrete formations and to compositions capable of providing said inhibition without imparting significant set retardation to the treated concrete.
One of the major disadvantages of conventional concrete compositions is that they tend to shrink during drying of the composition. This shrinkage results in cracks and other defects in the resultant structure. The cracks cause both appearance and physical defects to the structure. Although the magnitude of the shrinkage is normally small, it is of extreme importance. Such shrinkages give rise to internal and external stresses which cause formation of cracks. The largest changes normally take place during the early life of the structure.
The resultant cracks provide means of seepage of water in and through the structure. Water entry further deteriorates the structure through freeze-thaw pressures exerted by the water on the cement composition and by corrosion of metal reinforcing elements within the structure.
Various attempts have been made without success to vary cement-based compositions, per se, to overcome the shrinkage problem. These attempts included varying the properties of the cement, varying the methods of manufacture of a concrete mix and varying the ballast material used to form the resultant concrete composition. None of these attempts have resulted in a satisfactory solution.
Various admixtures have been proposed as useful in reducing shrinkage and the resultant cracking. For example Japanese Laid-Open Applications 81/37259 and 87/10947 disclose the use of alcohol-alkylene oxide and alkylphenol-alkylene oxide adducts as useful for this purpose. It was found that these materials must be used in large dosages which cause their usage to be expensive in order to provide the desired result. Lower alcohols as C.sub.4 -C.sub.6 alkyl alcohols (See U.S. Pat. No. 5,181,961) have also been suggested but these materials tend to be readily leached out by wet conditions which may be encountered. Further, such lower alcohols have high vapor pressures at ambient conditions and, therefore, are difficult to handle.
Further, various primary polyols have been suggested as a crack control agent. For example, Japanese Laid-Open Application 55-027819 discloses primary diol compounds of the formula RC(CH.sub.2 OH).sub.2 CH.sub.3, such as neopentylglycol, as being useful to inhibit shrinkage; EPA 308,950 discloses terminal hydroxyl containing compounds of the formula C.sub.n H.sub.2n (OH).sub.2 with the value of n being 5-10 as suitable for reduction of shrinkage; Japanese Laid-Open Application 06-072749 discloses 1,6 hexanediols for the desired purpose; and Japanese Laid Open Application 06-072748 disclose 2,2,-dimethyl-1,3-propanediol (neopentylglycol) for the desired purpose.
It is highly desired to provide a method and an admixture for use therein which is capable of reducing shrinkage and resultant cracking of the cast concrete composition structure to high degrees.